Gasifier reactor internal coating

ABSTRACT

A gasifier comprising an interior wall on which a layer is applied or an interior wall protected by an assembly of blocks, said layer or said blocks having at least one region of a sintered material containing:
         i) at least 25% by weight of chromium oxide Cr 2 O 3 ; and   ii) at least 1% by weight of zirconium oxide, wherein at least 20% by weight of said zirconium oxide ZrO 2  is stabilized in the cubic and/or quadratic form.

This patent application is a continuation-in-part of application Ser.No. 11/166,275, filed Jun. 27, 2005, now allowed, which claims priorityto French patent application no. FR/05/02529, filed Mar. 15, 2005. Thecontents of the above-referenced applications are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a gasifier reactor internal coating.

2. Background of the Invention

There is known in the art in particular a gasifier used to gasify coal.The coal gasification process, that has been known in the art for aroundfifty years, is currently experiencing strong growth because it can beused, starting from highly diverse hydrocarbon materials, for examplecoal, petroleum coke, and even heavy oils to be recycled, to producesynthesis gases serving as an energy source and as basic compounds forthe chemical industry. This process also eliminates unwanted components,for example NOx, sulfur or mercury, before discharge into theatmosphere.

The principle of gasification consists in controlled partial combustion,under pressure and in a steam or oxygen atmosphere, at a temperaturefrom approximately 1000° C. to approximately 1600° C.

There exist different types of reactor, known as “gasifiers”, withfixed, fluidized or driven beds. These reactors differ in the mode ofintroduction of the reactants, the manner in which the fuel and theoxidizer are mixed, the temperature and pressure conditions, and themethod of evacuating liquid residual slag or ash resulting from thereaction.

The article “Refractories for Gasification” published in the journal“Refractories Applications and News”, Volume 8, Number 4, July-August2003, written by Wade Taber of the Energy Systems department of theSaint-Gobain Industrial Ceramics Division, describes the structure of agasifier internal coating. The gasifier is coated with various layers ofrefractory products capable of withstanding the conditions oftemperature, pressure and chemical environment to which they aresubjected during gasification. The layers of refractory products thusprotect the metal interior wall of the gasifier from heat and fromcorrosion by gases and slag.

The refractory product at the hot face is more particularly subjected toerosion and chemical attack by ash or slag, which leads to theinfiltration of compounds from the liquefied ash or slag into the poresof the refractory product. As a result of erosion and thermal cycling,this infiltration can cause spalling of the coating, and finally toshutting down of the reactor.

To increase the service life of refractory coatings, researchers haveattempted to increase their thickness. However, this solution has thedrawback of reducing the usable volume of the gasifier and therefore itsyield.

James P. Bennett, in the article “Refractory liner used in slagginggasifiers” published in the journal “Refractories Applications andNews”, Vol 9, Number 5, September/October 2004, pages 20-25, explainsthat the service life of current gasifier refractory coatings, inparticular in air-cooled systems, is very limited despite their highcontent of chromium oxide. He mentions in particular the report by S. J.Clayton, G. J. Stiegel and J. G. Wimer “Gasification Technologies,Gasification Markets and Technologies—Present and future, an IndustryPerspective”, US DOE report DOE/FE 0447, July 2002.

There is therefore a requirement for a refractory coating adapted toresist the corrosion encountered in gasifiers more effectively and moredurably than prior art products.

The object of the invention is to satisfy this requirement.

SUMMARY OF THE INVENTION

According to the invention, the above object is achieved by means of agasifier internal refractory coating having at least one region of asintered material containing at least 45% by weight of chromium oxide(Cr₂O₃) and at least 1%, preferably at least 2%, and more preferably atleast 3%, by weight of zirconium oxide (ZrO₂), at least 20%, preferablyat least 30%, by weight of said zirconium oxide (ZrO₂) being stabilizedin the cubic and/or quadratic form.

As will emerge in more detail in the remainder of the description,surprisingly, the presence of at least 1% zirconium oxide of which atleast 20% by weight is stabilized in the cubic and/or quadratic formreduces infiltration and attack by slag without degrading the otherfunctional properties of the coating.

Said coating material of the invention preferably has one or more of thefollowing optional features:

-   -   At least 60% of the zirconium oxide is stabilized in the cubic        and/or quadratic form.    -   Said material contains at least one dopant, stabilizing or not        stabilizing the zirconium oxide, selected from CaO, MgO, Y₂O₃        and TiO₂, the preferred dopant being CaO. The content of calcium        oxide (CaO) of said material is preferably less than 1.0% by        weight. The dopant preferably stabilizes the zirconium oxide, at        least in part.    -   The content of zirconium oxide (ZrO₂) is greater than 4.5%,        preferably greater than 6% by weight, and/or less than 7% by        weight.    -   The content of chromium oxide (Cr₂O₃) is greater than 60% by        weight and preferably greater than 80% by weight.    -   Said material has an aluminum oxide (Al₂O₃) content greater than        1% by weight, preferably greater than 2% by weight, and/or less        than 10% by weight, preferably less than 5% by weight,        preferably less than 3.5% by weight.    -   Said material has a silica content greater than 0.5% by weight,        preferably greater than 1% by weight, and/or less than 3% by        weight, preferably less than 1.5% by weight.    -   The sum of the contents of oxides of chromium (Cr₂O₃), zirconium        (ZrO₂), aluminum (Al₂O₃), silicon (SiO₂) and calcium (CaO) is        greater than 95%, preferably greater than 98%, by weight, the        other constituents of the product being impurities. The        impurities conventionally comprise iron essentially in the form        of Fe₂O₃ and oxides of alkali metals such as Na₂O and K₂O. Such        contents of impurities are not considered to call into question        the advantages obtained from using the material.    -   The structure of the material features a granulate of chromium        oxide bound by a matrix comprising grains including zirconium        oxide and a dopant selected from CaO, MgO, Y₂O₃ and TiO₂, the        dopant, stabilizing or not stabilizing the zirconium oxide, the        percentage of zirconium oxide contained in said grains being        greater than 1%, preferably greater than 2.5%, by weight        relative to the weight of the material. The dopant content in        the grains containing zirconium oxide and a dopant is preferably        from 1% to 8% by weight relative to the weight of said grains.    -   The material takes the form of a layer applied to the interior        wall of a reactor of the gasifier or of an assembly of blocks        arranged to protect said wall. The whole of the layer or all the        blocks of the assembly preferably consist(s) of a material such        as that defined hereinabove.

In the present description, all percentages are percentages by weightunless otherwise indicated.

The composition of the slags in gasifiers typically consists of SiO₂,FeO or Fe₂O₃, CaO and Al₂O₃. It may also include other oxides derivedfrom products feeding the reactor. The base indexB=(CaO+MgO+Fe₂O₃)/(Al₂O₃+SiO₂) is typically about 0.6 and the ratioC/S=CaO/SiO₂ is typically 0.4, the contents being expressed aspercentages by weight.

Wang Zhe, as reported in the paper “Application of ZrO₂ in high Cr₂O₃low cement castable refractories for Refuse Melter” published in theproceedings of the 8th Biennial UNITEC Congress “Worldwide ConferenceRefractories ECO Refractory For The Earth” held from 19-22 Oct. 2003 inOsaka (Japan), studied the behavior of products with high chromium oxideand aluminum oxide contents, containing no silicon oxide, in relation tocorrosive slags encountered in furnaces for incineration of domestic orindustrial waste. The addition of a highly stabilized zirconia in cubicform representing from 3.2% to 6.4% of the total composition isdescribed as unfavorable to resistance to dissolution by the slags citedin the above publication. However, incineration furnace slags are verydifferent from those of gasifiers, as they have the followingcharacteristics: B index of approximately 1.2; C/S ratio ofapproximately 1.5.

A coating must be adapted to the corrosive conditions that itencounters. Thus it cannot be expected that a coating known to beresistant to certain corrosive conditions will be equally resistant whensubjected to other corrosive conditions. Thus it is found that materialsconforming to the invention include the materials described by Wang Zheas ineffective for waste incineration furnaces. Surprisingly, theinventors have discovered that these materials are effective in anapplication to a gasifier coating.

In applications such as glassmaking furnaces or iron and steel furnaces,as described in the patent EP 0 404 610, for example, there are known inthe art products consisting of zirconium oxide and chromium oxide. Theseproducts contain zirconium oxide in a proportion from 1% to 9% by weightrelative to the total composition. According to the above patent, it isessential that at least 80% of the zirconium oxide be in the monoclinicform, monoclinic zirconium being described as the “key ingredient” forimproving resistance to thermal shocks. Surprisingly, in the light ofthis teaching, the inventors have discovered that, in the application toa gasifier coating, the presence of zirconium oxide stabilized to atleast 20% is, on the contrary, advantageous.

Zirconium oxide can be stabilized by means of a stabilizing dopantand/or by heat treatment at very high temperature (typically greaterthan 1700° C.). According to the invention at least 20% by weight of thezirconium oxide is stabilized in the cubic and/or quadratic form.

A dopant selected from CaO, MgO, Y₂O₃ and TiO₂, acting or not acting asa stabilizer, is preferably present in the coating material of theinvention.

The refractory coating material of the invention consists of one or moregranulates, i.e. particles having a particle size greater than 150 μm,surrounded by a binder matrix.

The granulates may have diverse chemical compositions, in particularthey can consist of chromium oxide, the total content of chromium oxideof the material being at least 45% by weight.

The binder matrix comprises grains, i.e. particles having a particlesize less than 150 μm, including zirconium oxide and a dopant. Accordingto the invention, the zirconium oxide alone present in these grainspreferably represents more than 2.5% of the total weight of thematerial. In these grains, the dopant may have the function ofstabilizing the zirconium oxide or not. The binder matrix may furthercomprise other grains, in particular grains of zirconium oxide with nodopant.

The coating of the invention may be fabricated in the form of a layerobtained from a non-worked product or in the form of an assembly ofrefractory blocks.

To fabricate a coating in the form of a layer, a base mixture isprepared of particles of chromium oxide and zirconia, and possibly otheroxides, in proportions determined as a function of the composition ofthe required material. The dopant may be added to the mixture and/or beincluded with the zirconia, as a stabilizer. Forming additives may beadded to facilitate use, preferably in a proportion of less than 7%.

The manner of determining the proportions of the constituents of thebase mixture is well known to the person skilled in the art. Inparticular, the person skilled in the art knows that the chromium,aluminum and zirconium oxides present in the base mixture are found inthe sintered refractory material. Certain oxides of this material canalso be introduced by the additives. The composition of the base mixturemay therefore vary, in particular as a function of the quantities andthe nature of the additives present.

The chromium oxide may be added in the form of a mixture of sintered orfused chromium oxide particles. The aluminum oxide may be added in theform of a mixture of calcined or reactive particles of alumina, or evenof white corundum. The zirconium oxide may be added in the form ofcommercially available unstabilized zirconia and/or in the form ofstabilized zirconia, for example zirconia from Unitec, in powder form.

A powder is made up of particles of which 90% by weight have a particlesize less than 150 μm.

The base mixture preferably includes at least 0.2% by weight ofstabilized zirconia powder.

The base mixture preferably includes:

-   -   at least 60% of a particular mixture based on oxides of which at        least 90% by weight consists of particles having a particle size        greater than 150 microns but less than 20 mm;    -   less than 40% of a mixture of particles, at least 90% by weight        of the particles having a particle size less than 150 μm;    -   less than 7% of one or more forming additives well known to the        person skilled in the art.

The base mixture is preferably homogenized and conditioned. A mixture ofthis kind is advantageously ready for use and may be applied to theinterior wall of the reactor, for example by casting, vibrocasting orspraying, as a function of requirements and with great flexibility, andthen sintered in situ during preheating of the reactor, to produce arefractory coating of the invention. Sintering occurs at atmosphericpressure, in an oxidizing atmosphere and at a temperature from 1300% to1600° C.

To fabricate a coating of the invention, it is equally possible toassemble sintered blocks or prefabricated blocks which are then sinteredin service when the reactor is heated up.

To fabricate a sintered block, a fabrication method may be used thatincludes the following successive steps:

a) preparing a charge,

b) forming said charge in a mold,

c) casting said charge in the mold or compacting the charge by vibrationand/or pressing and/or pounding of said charge in the mold to form apreform,

d) removing the preform from the mold,

e) drying said preform, preferably in air or a moisture-controlledatmosphere, and preferably so that the residual moisture content of thepreform is from 0 to 0.5%,

f) firing said preform in an oxidizing atmosphere at a temperature from1300° C. to 1600° C. to form a fashioned refractory product, or asintered “refractory block”.

Like the base mixture described above, the charge includes oxidesdetermined as a function of the final composition of the block,precursors thereof and temporary forming additives.

The steps a) to f) are steps conventionally employed in the art tofabricate sintered products.

In step a), the manner of determining the quantities of the constituentsof the refractory product is well known to the person skilled in theart. In particular, the person skilled in the art knows that thechromium, aluminum and zirconium oxides present in the starting chargeare found in the fabricated refractory product. Certain oxides may alsobe introduced by the additives. For the same quantity of constituents ofthe sintered refractory product, the composition of the starting chargemay therefore vary, in particular as a function of the quantities andthe nature of the additives present in the charge.

The additives may be added to the starting charge to ensure that it issufficiently plasticized during the step b) of forming it and to confersufficient mechanical strength on the preform obtained at the end of thesteps d) and e). Non-limiting examples of additives that may be usedare:

-   -   organic temporary binders (i.e. binders that are eliminated        wholly or in part during drying and firing steps), such as        resins, derivatives of cellulose or lignone, polyvinyl alcohols;        the quantity of temporary binder is preferably from 0.1% to 6%        by weight relative to the weight of the particular mixture of        the charge;    -   forming agents such as stearates of magnesium or calcium;    -   hydraulic binders such as CaO aluminate cement;    -   deflocculating agents such as alkaline polyphosphates or        methacrylate derivatives;    -   sintering promoters such as titanium dioxide or magnesium        hydroxide;    -   clay type additives that facilitate use and assist sintering;        the above additives introduce alumina and silica and a few        oxides of alkali or alkaline-earth metals, even iron oxide,        depending on the type of clay.

The above quantities of additives are not limiting on the invention. Inparticular, the quantities conventionally used in sintering processesare appropriate.

The mixing of the various constituents of the charge continues until asubstantially homogeneous mass is obtained.

In the step b), the charge is formed and disposed in a mold.

In the step c), in the case of forming by pressing, a specific pressureof 400 to 800 kg/cm² is appropriate. Pressing is preferably effecteduniaxially or isostatically, for example by means of a hydraulic press.It may advantageously be preceded by an operation of manual or pneumaticramming and/or of vibration.

The drying of the step e) may be effected at a moderately hightemperature. It is preferably effected at a temperature from 110° C. to200° C. It conventionally takes from ten hours to one week, depending onthe format of the preform, continuing until the residual moisturecontent of the preform is less than 0.5%.

The dried preform is then fired (step f)). The firing time, fromapproximately three days to approximately 15 days from cold to cold,varies as a function of the materials but also as a function of the sizeand the shape of the parts. The firing cycle is preferably effected inthe conventional manner, in air, at a temperature from 1300° C. to 1600°C.

Surprisingly, the fashioned refractory product obtained at the end ofthe step f) has proved particularly resistant to the stressesencountered inside gasifier reactors, in particular to infiltration byfused ash or slag.

To fabricate a prefabricated block, the process steps a) to e) describedabove are used, but at least part of the firing step f) is effectedafter assembling the blocks in the reactor.

The blocks are assembled by means of appropriate expansion joints, usingtechniques well known to the person skilled in the art.

DESCRIPTION OF PREFERRED EXAMPLES

The following examples provide a non-exhaustive illustration of theinvention. The following raw materials were used for these examples:

-   -   particulate mixture of chromium oxide, with a purity of 98%        Cr₂O₃ by weight, and consisting of at least 90% by weight of        particles having a size greater than 20 microns but less than 20        mm,    -   pigmentary chromium oxide powder (>98% of Cr₂O₃) whose median        diameter (D50) is less than 2 microns,    -   calcined or micronized alumina powder with a median diameter of        5 microns,    -   monoclinic zirconia powder from ZIRPRO having the        characteristics set out in table 1 below (powder P1),    -   additives: magnesium or calcium stearates, temporary binders        (derivatives of cellulose or lignone), chemical binders        (phosphoric acid, derivatives of aluminum monophosphate),    -   stabilized zirconia powder from UNITEC, with the characteristics        set out in table 1 below (powder P2),    -   clay with a content of alumina >30%.

TABLE 1 P1 P2 D50 (μm) 3.9 20.0 ZrO₂ + HfO₂ (% by weight) 98.5 93.6 CaO(% by weight) 0.05 4.3 Crystalline phases Monoclinic Monoclinic (33%),(100%) Cubic + tetragonal (67%)

In a first step a), the raw materials were mixed and 3% water added.This was followed by the process steps:

b) forming the charge in a mold,

c) compacting the charge in the mold at a pressure of 600 kg/cm² to forma preform,

d) removing the preform from the mold,

e) drying the preform, in air, to obtain a residual moisture content ofthe material less than or equal to 0.5%,

f) firing said preform in an oxidizing atmosphere at a temperature from1400° C. to 1600° C. to form a fashioned refractory product.

The contents of aluminum, chromium, silicon and calcium oxides in thesintered final product were calculated from the chemical composition ofthe raw materials used for the starting charge.

Observation of the microstructure of the products of the invention showsthat they consist of a granulate of chromium oxide surrounded by abinder matrix that contains, for the products 2 to 5, grains ofZrO₂—CaO. Microprobe analysis identifies the content of the elements ofthe grains of ZrO₂—CaO coming from the powder P1 or P2.

The density and open porosity were measured on the products before anycorrosion had occurred and in accordance with the standard ISO 5017.

Further measurements were effected on products subjected, after the stepf), to corrosion representative of the service conditions suffered bythe hot face of gasifier coatings. This corrosion was obtained in thefollowing manner. Samples of the product to be tested with a size of25×25×180 mm³ placed in a furnace crucible were immersed in fused slagat a temperature of 1600° C. for four hours in an argon atmosphere. Thesamples were rotated at a speed of 2 rpm.

The slag used contained in particular:

SiO₂: approximately 30-50%

Al₂O₃: approximately 10-20%

Fe₂O₃ or FeO: 15-25%

CaO: approximately 10-20%

The base index B of this slag, i.e. the (CaO+MgO+Fe₂O₃)/(SiO₂+Al₂O₃)mass ratio, was typically of the order of 0.6. The CaO/SiO₂ mass ratiowas of the order of 0.4.

The following were evaluated: corrosion indicator, depth of penetrationof the CaO of the slag, zirconia depletion, and value of residualmodulus of rupture in bending after a thermal shock test.

The corrosion indicator is equal to the following ratio:

$100 \times \frac{\frac{\begin{matrix}{{{loss}\mspace{14mu}{of}\mspace{14mu}{section}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{sample}\mspace{14mu}{of}}\mspace{11mu}} \\{\;{{the}\mspace{14mu}{product}\mspace{14mu}{tested}\mspace{14mu}{at}\mspace{14mu}{the}\mspace{14mu}{atmosphere}}}\end{matrix}}{{slag}\mspace{14mu}{triple}\mspace{14mu}{point}}}{\frac{\begin{matrix}{{loss}\mspace{14mu}{of}\mspace{14mu}{section}\mspace{14mu}{of}\mspace{14mu}{the}\mspace{14mu}{reference}} \\{{sample}\mspace{14mu}{at}\mspace{14mu}{the}\mspace{11mu}{atmosphere}}\end{matrix}}{{slag}\mspace{14mu}{triple}\mspace{14mu}{point}}}$the loss of section resulting from the corrosive attack by the slagdescribed above and from the resulting dissolution of the refractoryproduct.

The corrosion indicator is therefore 100 for the reference product and avalue lower than 100 indicates better corrosion resistance than thereference product.

The depth of penetration of the CaO of the slag was measured by means ofa microprobe on a metallographic section.

The maximum depth to which the zirconia constituting the refractory hadbeen attacked and dissolved by the slag was measured by means of amicroprobe. This depth is referred to as “depletion”.

As the coating of the invention may be subjected in service to highstresses following thermal shocks, the inventors also measured thechange in the modulus of rupture in bending of the products subjected toa thermal shock.

The residual modulus of rupture in bending after a thermal shock testwas evaluated in accordance with the standard ISO 5014. It is listed as“Residual MOR” in table 2.

The table 2 below summarizes the results obtained.

TABLE 2 No. 1 2 3 4 5 Zirconia powder of the charge (% by weight) P1 7 00 0 0 P2 0 7 7 4.9 7.3 Calculated chemical composition of the sinteredproduct (% by weight) Cr₂O₃ 87 87 87 91 88 ZrO₂ 7.0 6.4 6.4 4.4 6.7Al₂O₃ 2.8 2.8 3.3 2.3 1.7 SiO₂ 0.4 0.4 1.2 0.9 0.9 CaO <0.1 0.3 0.3 0.20.3 Other properties of the sintered product (before corrosion) Apparentdensity (g/cm³) 4.25 4.24 4.30 4.20 4.23 Open porosity (%) 15.2 14.512.1 13.3 12.7 Measured infiltration of CaO and depletion caused bycorrosion Depletion of ZrO₂ (mm) 1.5 0 0 0.5 0.3 Depth of CaOinfiltration after >10 >10 3 5.4 >10 corrosion test (mm) Measureddissolution caused by corrosion Corrosion indicator 100 96 67 77 85Thermal shock resistance Residual MOR (MPa) 8.5 7 11 13 12

Composition No. 1 is the reference composition.

Table 2 indicates that:

-   -   The addition of stabilized zirconia containing CaO (compositions        2-3-4-5-6) reduces the depletion of zirconia, i.e. attacking of        the zirconia by the slag.    -   The presence of more than 0.5% silicon oxide is not harmful to        corrosion resistance.    -   The presence of aluminum oxide may be favorable to resistance to        calcium oxide infiltration, as is indicated by comparing        compositions 2 and 3.    -   The calcium oxide added in particular by the source of the        zirconia is not particularly harmful to the required properties.    -   The products of the invention have better corrosion resistance        than the reference product.    -   Composition 3 offers the best compromise for the required        properties and is preferred over all the others.

As is now clear, the coating of the invention advantageously reducesinfiltration and attack by the slags encountered in gasifier reactors,without other functional properties thereof being degraded.

New Developments

Starting from the above described invention, the inventors have furtherresearched products which could exhibit good resistance to corrosion, inparticular in the environment encountered in gasifiers, and goodmechanical properties.

According to new developments of the invention, the invention alsoconcerns a reactor, in particular a gasifier, comprising an interiorwall on which a layer is applied, or an interior wall protected by anassembly of blocks, said layer or said blocks having at least one regionof a sintered material containing

-   -   i) at least 25% by weight of chromium oxide Cr₂O₃; and    -   ii) at least 1% by weight of zirconium oxide, wherein at least        20% by weight of said zirconium oxide ZrO₂ is stabilized in the        cubic and/or quadratic form.

Indeed, the new researches have led to the discovery that very goodperformances may also be obtained with chromium oxide contents less than45%, as it is described here under.

Here under, this reactor, in particular gasifier, is designated as areactor “according to the new developments”.

The sintered material of a reactor according to the new developments mayhave one or several of the characteristics of the “wintered material ofthe gasifier internal refractory coating which is described here above”(i.e. already described in the original U.S. patent application Ser. No.11/166,275).

It may have one or more of the following optional characteristics, whichmay also be applied to the sintered material of the gasifier internalrefractory coating which is described here above:

-   -   The silica SiO₂ content is less than 9.5%, less than 9%, less        than 8%, less than 6%, less than 5%, or less than 4.5% by        weight.    -   The zirconium oxide ZrO₂ content is less than 25%, less than        20%, less than 15%, less than 10%, or less than 8%, by weight.    -   At least 70%, at least 95%, at least 90%, at least 95%, or even        substantially 100% of said zirconium oxide is stabilized in the        cubic and/or quadratic form.    -   The chromium oxide Cr₂O₃ content is more than 30%, more than        35%, more than 40%, more than 45%, more than 50%, more than 65%,        more than 70%, more than 75%, or even more than 85%, by weight.    -   The structure of the material features a granulate bound by a        matrix. The granulate may comprise chromium oxide, ZrO₂, Al₂O₃,        in particular corundum, Al₂O₃—ZrO₂—SiO₂, Al₃O₃—ZrO₂—SiO₂—Cr₂O₃        particles, or mixture of said particles. The content of Cr₂O₃ in        the granulate may be 15% or more, or 20% or more, on the basis        of the oxides of the sintered material (granulate+matrix). The        content of Cr₂O₃ in the matrix may be 10% or more, or 15% or        more, on the basis of the oxides of the sintered material.

In comparison with the sintered material of the gasifier internalrefractory coating which is described here above, the sintered materialof a reactor according to the new developments may have lower chromiumoxide Cr₂O₃ content. In particular, the difference in the chromium oxideCr₂O₃ content may be compensated by alumina, in particular corundumand/or zirconia and/or silica and/or magnesia and/or spinel and/or, moregenerally, crystallographic forms containing the element Aluminum. Thechoice of the substitute to the chromium oxide may depend on theintended application and in particular on the desired refractoriness.

In a preferred embodiment, the total content of Al₂O₃+ZrO₂ may be morethan 5%, more than 20%, more than 30%, more than 35%, and/or less than70%, less than 60%, or less than 50%, in percentages by weight on thebasis of the oxides.

Said layer or said blocks may be fabricated according to the methoddescribed here above used in order to fabricate a gasifier internalrefractory coating of the invention, provided that the starting chargeis adapted, according to the conventional practice. Preferably, thestarting charge contains more than 3%, preferably more than 5%, and/orless than 15%, preferably less than 10% of clay, in percentages on thebasis of the wet starting charge. In particular, the clay may be ballclay for instance or bentonite, or other natural aluminosilicates oreven artificial aluminosilicates.

Further New Developments

According to further new developments of the invention, the inventionalso concerns a sintered material containing:

-   -   at least 25% by weight of chromium oxide Cr₂O₃; and    -   at least 0.5% by weight and less than 9.5% of silica SiO₂; and    -   at least 1% by weight of zirconium oxide, at least 20% by weight        of said zirconium oxide ZrO₂ being stabilized in the cubic        and/or quadratic form.

Here under, this sintered material is designated as a “sintered materialaccording to the further new developments”.

As will emerge in more detail in the following description,surprisingly, the presence of silica may confer to a sintered materialaccording to the further new developments good resistance to corrosion,in particular in the environment encountered in gasifiers, and very goodmechanical properties.

This sintered material preferably has one or more of the followingoptional characteristics:

-   -   Said sintered material contains more than 30%, more than 35%,        more than 40%, more than 45%, more than 50%, and/or less than        70%, less than 60%, less than 55%, by weight, of chromium oxide        Cr₂O₃. A chromium oxide Cr₂O₃ content of about 53% by weight is        very well adapted.    -   Said sintered material contains more than 3%, more than 4%, more        than 5%, and/or less than 9%, less than 8%, less than 7%, less        than 6%, by weight, of silica SiO₂. A silica SiO₂ content of        about 5.5% by weight is very well adapted.    -   The total content of Al₂O₃+ZrO₂ may be more than 5%, more than        20%, more than 30%, more than 35%, and/or less than 70%, less        than 60%, or less than 50%, in percentages by weight on the        basis of the oxides.    -   Said sintered material contains more than 10%, more than 12%,        more than 15%, more than 17%, more than 19%, and/or less than        45%, less than 40%, less than 35%, less than 30%, less than 25%,        or less than 22%, by weight, of aluminum oxide Al₂O₃.    -   Said sintered material contains more than 10%, more than 12%,        more than 15%, more than 17%, more than 19%, and/or less than        45%, less than 40%, less than 35%, less than 30%, less than 25%,        or less than 22%, by weight, of zirconium oxide ZrO₂.    -   At least 30%, at least 40%, at least 50%, at least 60%, at least        70%, at least 80%, at least 90%, at least 95%, or even about        100%, by weight of said zirconium oxide ZrO₂ is stabilized in        the cubic and/or quadratic form.    -   Said sintered material contains at least one dopant, stabilizing        or not stabilizing the zirconium oxide, selected from CaO, MgO,        Y₂O₃, TiO₂, and rare earth oxides like CeO₂, Er₂O₃, La₂O₃, the        preferred dopant being CaO. The content of calcium oxide (CaO)        is preferably less than 1.0% by weight. The dopant preferably        stabilizes the zirconium oxide, at least in part.    -   The sum of the contents of oxides of chromium (Cr₂O₃), zirconium        (ZrO₂), aluminum (Al₂O₃), silicon (SiO₂) and calcium (CaO) is        greater than 95%, preferably greater than 98%, preferably        greater than 99%, by weight, the other constituents being        preferably impurities. The impurities conventionally comprise        iron essentially in the form of Fe₂O₃ and oxides of alkali        metals such as Na₂O and K₂O, in particular when clay is        introduced in the starting charge. Such contents of impurities        are not considered to call into question the advantages obtained        from using the sintered material.    -   The structure of the material features a granulate bound by a        matrix. The granulate may comprise chromium oxide, ZrO₂, Al₂O₃,        in particular corundum, Al₂O₃—ZrO₂—SiO₂, Al₃O₃—ZrO₂—SiO₂—Cr₂O₃        particles, or mixture of said particles. The content of Cr₂O₃ in        the granulate may be 15% or more, or 20% or more, on the basis        of the oxides of the sintered material (granulate+matrix). The        content of Cr₂O₃ in the matrix may be 10% or more, or 15% or        more, on the basis of the oxides of the sintered material.    -   The structure of the material features a granulate of chromium        oxide bound by a matrix comprising grains including zirconium        oxide and a dopant selected from CaO, MgO, Y₂O₃, TiO₂, and rare        earth oxides like CeO₂, Er₂O₃, La₂O₃, the dopant, stabilizing or        not stabilizing the zirconium oxide, the percentage of zirconium        oxide contained in said grains being greater than 1%, preferably        greater than 2.5%, by weight relative to the weight of the        material. The dopant content in the grains containing zirconium        oxide and a dopant is preferably from 1% to 8% by weight        relative to the weight of said grains.    -   The material takes the form of a layer applied to the interior        wall of a reactor, in particular of the gasifier, or of an        assembly of blocks arranged to protect said wall. The whole of        the layer or all the blocks of the assembly preferably        consist(s) of a sintered material according to the further new        developments.

The sintered material according to the further new developments may befabricated according to the method described here above used in order tofabricate a gasifier internal refractory coating of the invention,provided that the starting charge is adapted, according to theconventional practice, so as to obtain this sintered material.Preferably, the starting charge contains between more than 3%,preferably more than 5%, and/or less than 15%, preferably less than 10%of clay, more preferably less than 7% in percentages on the basis of thewet starting charge. In particular, the clay may be ball clay forinstance or bentonite, or other natural aluminosilicates or evenartificial aluminosilicates.

The invention also concerns a reactor, and in particular a gasifier,comprising an interior wall on which a layer is applied, or an interiorwall protected by an assembly of blocks, said layer or said blockshaving at least one region of a sintered material according to thefurther new developments of the invention.

The following examples provide a non-exhaustive illustration of theinvention according to the further new developments. The same rawmaterials as the raw materials used for the examples 1 to 5 have beenused, excepted that the following raw materials were also used:

-   -   particulate mixture of particles ER2161, said particles mainly        being composed of chromium, aluminum and zirconium oxides, sold        by SEPR (France) with the following average composition: Al₂O₃:        28%, ZrO₂: 27%, Cr₂O₃: 27%, SiO₂: 15%, impurities: complement to        100%. This mixture comprises at least 90% by weight of particles        having a size greater than 20 microns and less than 20 mm;    -   particulate mixture of particles ER1681, said particles mainly        being composed of aluminum, zirconium and silicon oxides, sold        by SEPR (France) with the following average composition: Al₂O₃:        51%, ZrO₂: 32.5%, SiO₂: 15%, impurities: complement to 100%.        This mixture comprises at least 90% by weight of particles        having a size greater than 20 microns and less than 20 mm;    -   calcined alumina with a median diameter less than 150 μm.        Examples 6 to 10 were fabricated and tested in the same way as        examples 1 to 5.        The table 3 below summarises the results.

TABLE 3 N° 6 7 8 9 10 Zirconia powder in the starting charge (% byweight) P1 0 0 0 0 0 P2 6.6 6.6 6.6 6.6 6.6 Calculated chemicalcomposition of the sintered product (% by weight) Cr₂O₃ 41 42 53 53 42ZrO₂ 16 22 19 20 17 Al₂O₃ 39 27 25 20 29 SiO₂ 2.8 7.5 2.6 5.4 10.5 CaO<0.5 <0.5 <0.5 <0.5 <0.5 Other properties of the sintered product beforecorrosion Apparent density (g/cm³) 3.80 3.81 4.00 4.02 3.78 Openporosity (%) 13.2 12.5 13.5 13.3 13.0 Measured infiltration of CaO andZrO₂ depletion caused by corrosion Depletion of ZrO₂ (mm) 0.8 0.5 0.50.3 n.m Depth of CaO 7.1 6.2 5.4 4.1 >10 infiltration after corrosiontest (mm) Measured dissolution caused by corrosion Corrosion indicator180 170 150 145 230 Thermal shock resistance Residual MOR (Mpa) 11 25 1028 17 n.m = not measured

The products 6 to 9 exhibit very good thermal shock resistance and acorrosion indicator which is much less than the corrosion indicator ofproduct 10.

Table 3 also shows that products 7 and 9, comprising more than 3% ofsilica are preferable to products 6 and 8, respectively.

Indeed, the products 7 and 9 of the invention may be compared to theproducts 6 and 8, respectively, which present similar chromium oxidecontents and similar densities. Table 3 shows that the products 7 and 9exhibit better resistance to corrosion, i.e. lower corrosion indicators.This is surprising since the products 7 and 9 have higher silica contentthan the products 6 and 8, respectively.

Moreover, advantageously the products 7 and 9 exhibit a lower depth ofCaO infiltration, less zirconia depletion and higher residual MORcompared to the products 6 and 8, respectively.

The product 9 is preferred.

A comparison of example 10 with example 7, presenting similar chromiumoxide content, shows that silica content higher than 10% is detrimentalto the corrosion resistance. In particular, the corrosion indicator andthe depth of CaO infiltration of example 10 are significantly higher.

Of course, the present invention is not limited to the embodimentsdescribed, which are given by way of illustrative and non-limitingexample.

1. A sintered material, comprising: at least 25% by weight of chromiumoxide Cr₂O₃; at least 0.5% by weight and less than 9.5% of silica SiO₂;and at least 1% by weight of zirconium oxide, at least 30% by weight ofsaid zirconium oxide ZrO₂ being stabilized in the cubic and/or quadraticform, wherein said sintered material is a granulate bound by a matrix.2. The sintered material of claim 1, containing more than 35% by weightof chromium oxide Cr₂O₃.
 3. The sintered material of claim 1, containingmore than 45% by weight of chromium oxide Cr₂O₃.
 4. The sinteredmaterial according to the claim 1, containing less than 70% by weight ofchromium oxide Cr₂O₃.
 5. The sintered material according to the claim 1,containing more than 3%, by weight, of silica SiO₂.
 6. The sinteredmaterial according to the claim 1, containing more than 5%, by weight,of silica SiO₂.
 7. The sintered material according to the claim 1,containing less than 8%, by weight, of silica SiO₂.
 8. The sinteredmaterial according to the claim 1, further comprising more than 10%, byweight, of aluminum oxide Al₂O₃.
 9. The sintered material according toclaim 8, containing more than 15%, by weight, of aluminum oxide Al₂O₃.10. The sintered material according to claim 1, further comprising lessthan 45%, by weight, of aluminum oxide Al₂O₃.
 11. The sintered materialaccording to claim 10, containing less than 25%, by weight, of aluminumoxide Al₂O₃.
 12. The sintered material according to claim 1, containingmore than 10%, by weight, of zirconium oxide ZrO₂.
 13. The sinteredmaterial according to claim 1, containing more than 15%, by weight, ofzirconium oxide ZrO₂.
 14. The sintered material according to claim 1,containing less than 45%, by weight, of zirconium oxide ZrO₂.
 15. Thesintered material according to claim 1, containing less than 25%, byweight, of zirconium oxide ZrO₂.
 16. The sintered material according toclaim 1, in which at least 60% by weight of said zirconium oxide ZrO₂ isstabilized in the cubic and/or quadratic form.
 17. The sintered materialaccording to claim 1, containing at least one dopant, not stabilizingthe zirconium oxide, selected from the group consisting of CaO, MgO,Y₂O₂, and TiO₂, and rare earth oxides selected from the group consistingof CeO₂, Er₂O₃, and La₂O₃.
 18. The sintered material according to claim1, the sum of the contents of chromium oxide Cr₂O₃, zirconium oxideZrO₂, aluminum oxide Al₂O₃, silica SiO₂ being greater than 95% byweight.
 19. The sintered material according to claim 1, wherein thetotal content of Al₂O₃+ZrO₂ is more than 5% and less than 70%, inpercentages by weight on the basis of the oxides.
 20. The sinteredmaterial according to claim 1, wherein the total content of Al₂O₃+ZrO₂is more than 35%, in percentage by weight on the basis of the oxides.21. The sintered material according to claim 1, comprising a granulatebound by a matrix, the content of Cr₂O₃ in the granulate being 15% ormore and the content of Cr₂O₃ in the matrix being 10% or more, inpercentages by weight on the basis of the oxides of the sinteredmaterial.
 22. The sintered material according to claim 1, wherein thestructure of said material comprises a granulate of chromium oxide boundby a matrix comprising grains including zirconium oxide and a dopantselected from the group consisting of CaO, MgO, Y₂O₃, and TiO₂, and rareearth oxides selected from the group consisting of CeO₂, Er₂O₃, andLa₂O₃, the dopant, stabilizing or not stabilizing the zirconium oxide,the percentage of zirconium oxide contained in said grains being greaterthan 1%, by weight relative to the weight of the sintered material. 23.A reactor comprising an interior wall on which a layer is applied or aninterior wall protected by an assembly of blocks, said layer or saidblocks having at least one region of a sintered material according toclaim
 1. 24. The reactor according to claim 23 in the form of agasifier.
 25. A method to fabricate the sintered material according toclaim 1, comprising the sintering of a starting charge, wherein thestarting charge contains more than 3% and less than 15% of clay, inpercentages on the basis of the wet starting charge.
 26. The sinteredmaterial according to claim 1, wherein said sintered material comprisesa sintered base mixture, said base mixture comprising a powder of fineparticles of stabilized zirconia.
 27. The sintered material according toclaim 26, wherein the zirconia of said fine particles is stabilized witha dopant selected from the group consisting of CaO, MgO, Y₂O₂, and TiO₂,and rare earth ozides selected from the group consisting of CeO₂, Er₂O₃,and La₂O₃.
 28. The sintered material according to claim 1, wherein saidsintered material comprises a sintered base mixture including at least60% of a particular mixture, based on oxides, of which at least 90% byweight consists of particles, having a particle size greater than 150microns and less than 20 mm.
 29. The sintered material according toclaim 1, wherein the content of Cr₂O₃ in the granulate is 15% or more.30. The sintered material according to claim 1, wherein the sinteredmaterial has an open porosity of 12.1% or more.
 31. The sinteredmaterial according to claim 1, wherein said sintered material comprisesa sintered base mixture, said base mixture including less than 40% of aparticular mixture of which at least 90% by weight consists of particleshaving a particle size less than 150 μm.